Fix infinite entity expansion by detecting circular references#312
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naitoh wants to merge 1 commit intoruby:masterfrom
Open
Fix infinite entity expansion by detecting circular references#312naitoh wants to merge 1 commit intoruby:masterfrom
naitoh wants to merge 1 commit intoruby:masterfrom
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## Why?
Fix an issue where a `stack level too deep (SystemStackError)` error caused by a circular reference was not detected as an appropriate error.
```
require 'rexml/parsers/streamparser'
require 'rexml/streamlistener'
source = <<~XML
<!DOCTYPE root [
<!ENTITY x "&x;">
]>
<root>&x;</root>
XML
listener = Class.new { include REXML::StreamListener }.new
REXML::Parsers::StreamParser.new(source, listener).parse
```
- before
```
lib/rexml/parsers/baseparser.rb:544:in 'REXML::Parsers::BaseParser#entity': stack level too deep (SystemStackError)
```
- after
```
lib/rexml/parsers/baseparser.rb:543:in 'REXML::Parsers::BaseParser#entity': Detected an entity reference loop: x (RuntimeError)
```
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Pull request overview
This PR adds circular entity-reference detection to prevent unbounded recursive expansion (previously resulting in SystemStackError) during streaming-style parsing.
Changes:
- Track the current entity-expansion chain in
REXML::Parsers::BaseParserand raise a clear error when a loop is detected. - Extend
BaseParser#unnormalize/#entityto thread the expansion state through nested expansions. - Add regression tests covering direct/indirect circular references (including a long entity value) via
StreamParser.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
lib/rexml/parsers/baseparser.rb |
Adds loop detection during entity expansion by propagating an “currently expanding” set through recursive unnormalization. |
test/test_entity.rb |
Adds regression tests ensuring circular entity references raise an appropriate error instead of stack overflow. |
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|
|
||
| record_entity_expansion | ||
| unnormalize( value, entities ) | ||
| unnormalize( value, entities, nil, (expanding || Set.new) | [reference] ) |
Comment on lines
541
to
+546
| value = entities[ reference ] | ||
| return if value.nil? | ||
| raise "Detected an entity reference loop: #{reference}" if expanding&.include?(reference) | ||
|
|
||
| record_entity_expansion | ||
| unnormalize( value, entities ) | ||
| unnormalize( value, entities, nil, (expanding || Set.new) | [reference] ) |
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Why?
Fix an issue where a
stack level too deep (SystemStackError)error caused by a circular reference was not detected as an appropriate error.